The present invention relates to a polyurethane adhesive, a method of using it for adhesion, and a use of the mixture; and in particular, the present invention relates to a polyurethane adhesive that is useful in adhering plastics, metals, and the like, a method of using it for adhesion, and a use of the mixture.
In recent years, multi-layered composite films in which plastic films such as polyethylene, polypropylene, polyamide, polyester, vinyl chloride, vinylidene chloride, or the like, or alternatively, a combination of a plastic film and metallic foil such as aluminium foil are laminated in two-, three-, or four-plus layers, have been developed and used in various ways as a packaging material for food and luxuries.
Furthermore, in order to keep the freshness and flavor of food products and preserve these food products over a long period of time, higher performance, multi-layered composite films are required, and therefore, improvements for an adhesive used in laminating are strongly desired.
In particular, an adhesive for use in multi-layered composite films for packaging retort food products or food products requiring high-temperature sterization, must exhibit superior properties with regard to an initial adhesion strength, permanent adhesion strength, hot water resistance, fatigue resistance, acid resistance, and the like, as well as high-speed lamination.
Hitherto, a polyurethane adhesive has been used for the aforementioned purposes, however, its properties in hot water resistance, heat resistance, and resistance to contents, are inferior. For example, when food containing vinegar is packaged and disinfected with water at a high temperature, the adhesion strength between the aluminium foil and plastics weakens, leading to peeling and loss of function as a multi-layered composite film.
As the aforementioned polyurethane adhesive, Japanese Published Examined Patent Application, No. 25989/92 discloses a polyurethane adhesive comprising a poly(xcex2-methyl-xcex4-valerolactone)polyol and the like, and an organic polyisocyanate.
Additionally, Japanese Published Unexamined Patent Application, No. 6075/88 discloses a polyurethane adhesive comprising a polymer polyol derived from 3-methyl-1,5-pentanediol, and an organic polyisocyanate.
In addition, Japanese Published Unexamined Patent Application, No. 182387/88 discloses a polyurethane adhesive comprising a polymer polyol derived from 2-methyl-1,8-octanediol, and an organic diisocyanate.
Additionally, Japanese Published Unexamined Patent Application, No. 262859/93 discloses an adhesive comprising a polyester polyol derived from a diol possessing an alkyl side chain, and a hardening agent; and Japanese Published Unexamined Patent Application, No. 81414/92 discloses an adhesive comprising a polyester polyol polyurethane derived from a diol possessing an alkyl side chain. However, the aforementioned publications neither disclose concrete technological details nor disclose any specific disclosure with regard to a polyurethane derived from a 2,4-dialkyl-1,5-penetanediol.
In addition, WO96/09334 discloses a polyurethane comprising a polyester polyol derived from a 2,4-dialkyl-1,5-pentanediol, and an organic polyisocyanate; however, this document does not disclose its use as an adhesive.
It is an object of the present invention to provide a polyurethane adhesive that is particularly useful in manufacturing multi-layered composite films which are formed by means of laminating various plastic films, metallic foil, and the like.
The present invention provides an adhesive comprising a polyester polyol or polyurethane polyol possessing structural units represented by the following general formula (I) within its molecular structure, and an organic polyisocyanate in which the isocyanate groups may be protected (hereinafter, said organic polyisocyanate in which the isocyanate groups are unprotected is sometimes referred to simply as an organic polyisocyanate): 
wherein R1 and R2 are the same or different and each represents lower alkyl.
Additionally, the present invention provides a method of mixing a polyester polyol or polyurethane polyol, possessing the structural units represented by the aforementioned general formula (I), and an organic polyisocyanate in which the isocyanate groups may be protected, and using the mixture for adhesion. Furthermore, the present invention provides a use of a mixture of a polyester polyol or polyurethane polyol, possessing the structural units represented by the aforementioned general formula (I), and an organic polyisocyanate in which the isocyanate groups may be protected.
In the definition of the aforementioned general formula (I), the lower alkyl means a linear or branched chain alkyl having 1 to 8 carbon atoms, examples of which may include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isoamyl, neopentyl, 2-pentyl, 3-pentyl, hexyl, heptyl, octyl, and the like.
The polyester polyol, a component of the adhesive of the present invention, is a polyester possessing the structural units represented by the aforementioned general formula (I) as repeating units in the main chain. Preferably, both terminal groups of said polyester are normally hydroxyl groups.
The structural units represented by the aforementioned general formula (I) are formed by esterification of a 2,4-dialkyl-1,5-pentanediol and a dicarboxylic acid, or transesterification of a 2,4-dialkyl-1,5-pentanediol and a dicarboxylic acid ester, or the like.
In other words, an example of the method for preparation is a method carrying out esterification of a diol containing a 2,4-dialkyl-1,5-pentanediol, which is a constituent that provides structural units represented by the general formula (I), and a dicarboxylic acid, according to a conventional method. For example, a diol containing a 2,4-dialkyl-1,5-pentanediol and a dicarboxylic acid is heated to 150-250xc2x0 C. in the presence of a catalyst for esterification, if necessary. The pressure is reduced to 10-15 mmHg at the same temperature when the acid number of the reaction mixture reaches about 15 (KOH mg/g), and the esterification reaction is further continued. When the acid number of the reaction mixture reaches about 0.3 (KOH mg/g), the reaction is stopped and the mixture is cooled, to obtain the desired polyester polyol.
Additionally, the other example of the method for preparing the polyester polyol is a method carrying out transesterification of a diol containing a 2,4-dialkyl-1,5-pentanediol and a lower alkyl ester of dicarboxylic acid such as a methyl ester, an ethyl ester, or the like, according to a conventional method.
In the starting materials for the esterification reaction, when adding an organic polyisocyanate to a polyester polyol for a use as an adhesive, the molar ratio of all dicarboxylic acids or the lower alkyl esters of the dicarboxylic acids to all diols is 0.90-1.20, and preferably 0.95-1.10. Additionally, when preparing the polyester polyol as a starting material of the polyurethane polyol, the molar ratio of all dicarboxylic acids or the lower alkyl esters of the dicarboxylic acids to all diols is 0.1-1.0, and preferably 0.5-1.0, while the preferred terminal groups of the polyester are normally hydroxyl groups.
Specific examples of the 2,4-dialkyl-1,5-pentandiol may include 2,4-dimethyl-1,5-pentanediol, 2-ethyl-4-methyl-1,5-pentanediol, 2-methyl-4-propyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, 2-ethyl-4-propyl-1,5-pentanediol, 2,4-dipropyl-1,5-pentanediol, 2-isopropyl-4-methyl-1,5-petanediol, 2-ethyl-4-isopropyl-1,5-pentanediol, 2,4-diiosopropyl-1,5-pentanediol, 2-isopropyl-4-propyl-1,5-pentanediol, 2,4-dibutyl-1,5-pentanediol, 2,4-dipentyl-1,5-pentanediol, 2,4-dihexyl-1,5-pentanediol, and the like. Among these examples, 2,4-diethyl-1,5-pentanediol is preferably used.
The 2,4-dialkyl-1,5-pentandiol can be prepared according to a known method such as the method disclosed in Japanese Published Unexamined Patent Application, No. 48642/96 or EP807617A.
A portion of the 2,4-dialkyl-1,5-pentanediol used as a starting material of the polyester polyol may be replaced with other diols. Examples of other diols may include ethylene glycol, propylene glycol, diethylene glycol, 1,4-butanediol, 1,5-pentanediol, neopentylglycol, 1,6-hexanediol, 2-butyl-2-ethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2-methyl-1,8-octanediol, 1,9-nonanediol, 1,4-bis(xcex2-hydroxyethoxy)benzene, and the like.
In addition, a small amount of alcohols other than the aforementioned diol, such as a monohydric alcohol including methyl alcohol, ethyl alcohol, isopropyl alcohol, or the like, and a polyhydric alcohol including trimethylol propane, glycerin, or the like, may be used together.
When using the other diol or alcohol as stated above, the usage amount of the 2,4-dialkyl-1,5-pentanediol is preferably 30 mol % or more in all amount of alcohol content in the starting materials for the esterification reaction, and more preferably 50 mol % or more.
Examples of the dicarboxylic acid for preparing the polyester polyol may include succinic acid, adipic acid, azelaic acid, maleic acid, fumaric acid, phthalic acid, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, and the like, which may be used alone or in combination of two or more.
When adding an organic polyisocyanate to the polyester polyol for a use as an adhesive, the number average molecular weight of the polyester polyol is preferably 10,000-120,000. The polyester polyol having a number average molecular weight in the above range contains a number of the structural units represented by the aforementioned general formula (I).
In addition, when reacting the polyester polyol with an organic diisocyanate to produce a polyurethane polyol, and subsequently adding an organic polyisocyanate to the polyurethane polyol for a use as an adhesive, the number average molecular weight of the polyester polyol is preferably 400-8,000, and more preferably 400-4,000. When the number average molecular weight of the polyester polyol exceeds the aforementioned range, a deterioration is observed in basic properties of an adhesive such as wetting to the adhered component, cohesion of the resin, or the like.
The polyurethane polyol, a component of the adhesive of the present invention, is obtained by urethane formation from a polyester polyol possessing the structural units represented by the aforementioned general formula (I). The terminal groups of the polyurethane polyol are preferably normally hydroxyl groups.
The aforementioned polyurethane polyol can be prepared according to a conventional method for preparing polyurethane. For example, the polyester polyol obtained according to the aforementioned method is, after a chain extender is added, if necessary, heated to 60-100xc2x0 C. in advance. Subsequently, an organic diisocyanate is added such that the molar ratio of the isocyanate groups of the organic diisocyanate to the total active hydrogens in the polyester polyol and a chain extender becomes 0.90-1.00, and the resultant mixture is heated at 80-180xc2x0 C. for 10 minutes to 5 hours, to obtain the desired polyurethane polyol. In preparing the polyurethane polyol, a catalyst may be used, if necessary, in order to accelerate the reaction, and examples of the catalyst may include metallic salts of organic acids such as tin octylate, and the like, organic tertiary amine such as triethylene diamine, and the like, and the like. The usage amount of the catalyst is 0.1-3.0% by weight of the total amount of the polyester polyol, the chain extender, and the organic diisocyanate.
Examples of the organic diisocyanate compound for preparing the polyurethane polyol may include 4,4xe2x80x2-diphenylmethane diisocyanate, 2,6-tolylene diisocyanate, 1,6-hexamethylene diisocyanate, isophorone diisocyanate, 4,4xe2x80x2-dicyclohexylmethane diisocyanate, 1,3-xylylene diisocyanate, and the like, which may be used alone or in combinations of two or more. Furthermore, a small amount of polyfunctional polyisocyanates such as a compound in which 3 moles of 2,6-tolylene diisocyanate are added to 1 mol of trimethylol propane, and the like, may be used together.
Chain extenders include a lower-molecular compound possessing at least two active hydrogen atoms which react with the isocyanate groups, and preferably 2-10 active hydrogen atoms. Examples of the chain extender may include ethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentylglycol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-bis(xcex2-hydroxyethoxy)benzene, isophorone diamine, hydrazine, and the like. The usage amount of the chain extender to the amount of the polyester polyol is preferably a molar ratio of 0.1-10, and more preferably a molar ratio of 0.2-2.0.
When preparing the polyurethane polyol, it is possible to carry out the reaction in the presence of a solvent. The solvent may be added at any stage of the reaction. The polyurethane polyol prepared in a solvent may be used as a component of the adhesive without removing the solvent, according to the objective and use.
Preferred examples of the solvent may include acetone, methyl ethyl ketone, methyl n-propyl ketone, methyl isobutyl ketone, methyl acetate, ethyl acetate, butyl acetate, cyclohexanone, tetrahydrofuran, toluene, xylene, dimethylformamide, dimethylsulfoxide, butyl cellosolve, and the like. The polyurethane polyol is preferably soluble in these solvents.
A number average molecular weight of the polyurethane polyol is preferably 2,500-90,000, and more preferably 10,000-90,000.
The adhesive of the present invention can be obtained by mixing adhesive components such as the aforementioned polyester polyol or polyurethane polyol, an organic polyisocyanate in which the isocyanate groups may be protected, and the like. Furthermore, in the adhesive, the molar ratio of the protected or unprotected isocyanate group per 1 mole of the active hydrogen atom contained in the polyester polyol or polyurethane polyol is 1 mole or more.
In addition, a chain extender may be added, if necessary, and the aforementioned chain extenders may be used.
As a component of the adhesive of the present invention, a portion of the polyester polyol or polyurethane polyol may be replaced with a polyester polyol or polyurethane polyol derived from other diols. In this case, examples of the other diol may include the aforementioned, replaceable diols. In addition, the ratio of a 2,4-dialkyl-1,5-pentanediol in all amount of polyester polyols or in all amount of diols of starting materials for the polyurethane polyol is preferably 30 mol % or more, and more preferably 50 mol % or more.
In order to accelerate hardening, a catalyst for hardening may be added to the adhesive of the present invention, if necessary. Examples of the catalyst may include the aforementioned catalysts used in preparing the polyurethane polyol. The usage amount of the catalyst is 0.1-3.0% by weight to the total amount of the polyester polyol or polyurethane polyol, the chain extender, and the organic polyisocyanate.
A solvent may be added to the adhesive of the present invention, if necessary. Examples of the solvent may include the aforementioned solvents. When using a solvent, the solid content should be 20-80% by weight in order to form a uniform adhesive layer on the adhered object, and preferably 30-70% by weight.
As the organic polyisocyanate, a component of the adhesive of the present invention, an organic polyisocyanate conventionally used as a hardening agent for a polyurethane adhesive may be used, and an organic polyisocyanate having 3 or more isocyanate groups may be preferably used. When the organic polyisocyanates are the polyisocyanate having 3 or more isocyanate groups, the hardened material which the adhesive of the present invention provides is a cross-linked one.
Specific examples of the organic polyisocyanate may include diphenylmethane diisocyanate, 1,6-hexamethylene diisocyanate, a polymer of 1,6-hexamethylene diisocyanate, an adduct of 2,4-tolylene diisocyanate and prenzcatechol, tolylene diisocyanate, 1-chlorophenyl diisocyanate, 1,5-naphthylene diisocyanate, thiodipropyl diisocyanate, ethylbenzene-xcex1-2-diisocyanate, a dimer of 2,4-tolylene diisocyanate, 4,4xe2x80x2,4xe2x80x3-triphenylmethane triisocyanate, and the like. Preferred examples may include 3 or more functional compounds in which tolylene diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, or the like, is added to a polyhydric alcohol such as trimethylol propane, glycerin, pentaerythritol, hexanetriol, or the like. Among these compounds, a trifunctional isocyanate compound in which 3 moles of 2,6-tolylene diisocyanate are added to 1 mole of trimethylol propane is more preferably used. The aforementioned organic polyisocyanate is sold and can be purchased on the market. The organic polyisocyanate is used such that the equivalent ratio of all isocyanate groups to all active hydrogens in the polyester polyol or polyurethane polyol and chain extender is preferably 1-20, and more preferably 1-10. If the ratio is less than 1, the adhesive provides unsatisfactory adhesion strength by insufficiency of isocyanate groups. On the other hand, if the ratio is more than 20, the adhesive provides lack of the flexibility of an adhered object by excess of isocyanate groups.
The adhesive of the present invention is used normally as a dual-liquid type adhesive comprising a component containing the polyester polyol or polyurethane polyol, and a component containing the organic polyisocyanate. The component containing the polyester polyol or polyurethane polyol may include the aforementioned solvent, chain extender, catalyst for hardening, or the like, if necessary. In addition, the component containing the organic polyisocyanate may include the solvent, catalyst for hardening, or the like. The temperature for hardening the dual-liquid type adhesive of the present invention is preferably in the range from room temperature to 250xc2x0 C., and more preferably 30-100xc2x0 C.
The adhesive of the present invention can be used as a single-liquid type adhesive by using an organic polyisocyanate in which the isocyanate groups are protected. Examples of the organic polyisocyanate in which the isocyanate groups are protected may include prepolymers and blocked polyisocyanates with phenols, alcohols, oximes, or the like. Herein, the blocked polyisocyanate means an organic polyisocyanate in which the isocyanate groups are blocked with a phenolic hydroxyl group, an alcoholic hydroxyl group, or the like. The blocking groups of these blocked polyisocyanates are removed by heating to liberate the isocyanate groups. The liberated isocyanate groups react with hydroxyl groups in the polyester polyol or polyurethane polyol. The temperature for hardening is normally 80-150xc2x0 C. Furthermore, examples of a blocking agent, which blocks the isocyanate groups, may include phenols such as phenol, m-nitrophenol, p-chlorophenol, cresol, catechol, and the like; alcohols such as methanol, ethanol, ethylene chlorohydrin, and the like; oximes such as methyl ethyl ketoxime, cyclohexanone oxime, and the like; xcex5-caprolactam, ethyl malonate, ethyl acetone, ethyl acetoacetate, and the like. The blocked polyisocyanates can be obtained on the market, or alternatively, may also be synthesized according to a conventional method. The blocked polyisocyanate may be used according to the aforementioned usage conditions for the organic polyisocyanate.
Furthermore, the prepolymer of the organic polyisocyanate means an organic polyisocyanate in which terminal isocyanate groups are blocked by the polyester polyol, the polyurethane polyol, a multifunctional active hydrogen compound, or the like. Herein, examples of the multifunctional active hydrogen compounds may include compounds similar to the aforementioned chain extender. The adhesive containing the above prepolymer hardens at room temperature by the water content in the air. The aforementioned prepolymer can be synthesized according to a conventional method. The prepolymer can be used according to the aforementioned usage conditions for the organic polyisocyanate.
When using the adhesive of the present invention, the adhering condition is not particularly limited, however, the usage amount of the adhesive to the adhered object is preferably 0.1-10 g/m2, and more preferably, 1.5-4.5 g/m2.
The adhesive of the present invention is suitable for adhering all kinds of objects, for example, thermoplastic resin such as polyolefine (including polyethylene, polypropylene, and the like), polystyrene, ethylene-vinyl acetate copolymers or saponificated polymers thereof; vinyl chloride resin, polyester (including polyethylene terephthalate, polybutylene terephthalate), polyamide (including nylon), polyurethane, or the like; synthetic resin such as phenol resin, melamine resin, urea resin, or the like; natural rubber; metals such as aluminium, copper, iron, or the like; fibers such as mesh fabric, non-woven fabric, or the like; wood, glass, ceramic, or the like. In particular, the aforementioned adhesive is applicable to a wide variety of uses such as adhering packaging materials for food, pharmaceuticals, or the like, building materials, electrical parts, auto parts, fibers, lamination of plastics, or the like. In addition, the adhesive of the present invention is also suitable as an adhesive for use in laminating polyester film, polyamide film, or the likexe2x80x94metallic foil, such as aluminium foilxe2x80x94polyolefine film; or polyolefine filmxe2x80x94polyamide film, or the like, which is used as a packaging material for retort food products that requires disinfection treatment with hot water and preservation for a long time while containing vinegar, vegetable oil, or the like.
In addition, the adhesive of the present invention provides excellent processing properties and an initial adhesion strength, and the adhered object using the adhesive provides an excellent permanent adhesion strength, hot water resistance, flexibility, flexibility at low temperature, fatigue resistance, and the like.